Pyrolytic graphite alloys and method of making the same



M. BASCHE Sept. 2, 1969 PYROLYTIC GRAPHITE ALLOYS AND METHOD OF MAKINGTHE SAME Filed March 21, 1962 FIG! ' FIGZ INVENTOR. MALCOLM 303045 2)ATTOR EY United States Patent 3,464,843 PYROLYTIC GRAPHITE ALLOYS ANDMETHDD OF MAKING THE SAME Malcolm Basche, Newtonville, Mass, assignor,by mesne assignments, to Union Carbide Corporation, a corporation of NewYork Continuation-impart of application Ser. No. 124,440, July 17, 1961.This application Mar. 21, 1962, Ser. No. 181,313

Int. Cl. C23c 9/06 U.S. Cl. 11746 8 Claims This invention relates toalloys and more particularly to alloys comprising pyrolytic graphite andto methods of producing such alloys. This application is, in part, acontinuation of copending application Ser. No. 124,440, filed July 17,1961 now abandoned.

A principal object of the present invention is to provide novel alloyscomprising pyrolytic graphite and at least one metal and/ or metalloid.

Another object of the present invention is to provide one or moreprocesses for producing pyrolytic graphite alloys.

Still another object of the present invention is to provide novel alloyscomprising pyrolytic graphite and boron.

A still further object of the present invention is to provide new andimproved alloys comprising pyrolytic graphite and boron which may beused in heat shields.

Other objects of the invention will in part be obvious and will in partappear hereinafter.

The invention accordingly comprises the process involving the severalsteps and the relation and the order of one or more of such steps withrespect to each of the others, and the products possessing the featuresand properties which are exemplified in the following detaileddisclosure, and the scope of the application of which will be indicatedin the claims.

For a fuller understanding of the nature and objects of the invention,reference should be had to the following detailed description taken inconnection with the accompanying drawings wherein:

FIGURE 1 is a schematic, flow diagram illustrating a process forproducing pyrolytic graphite alloys; and

FIGURE 2 is a diagrammatic view of a halide generator which may be usedin production of pyrolytic graphite alloys.

It has been discovered that alloys comprising pyrolytic graphite and ametal such as, for example, a refractory metal as tungsten, hafnium orthe like, or alloys comprising pyrolytic graphite and a metalloid suchas, for example, boron or silicon can be produced if a gaseous metal ormetalloid compound, e.g. a halide is contacted with a gaseoushydrocarbon at a suitable temperature. Of the many pyrolytic graphitealloys which may be prepared in the above manner, alloys comprisingpyrolytic graphite and boron are of particular interest since it hasbeen found that such alloys exhibit very unusual characteristics.

For instance, the thermal conductivity of some of such alloys, issubstantially less than that exhibited by pyrolytic graphite itself ifthe thermal conductivity is measured in the c direction, that is, thedirection perpendicular to the surface of the deposit. It is also ofinterest to note that the electrical conductivity of such alloys issubstantially greater than that of ordinary pyrolytic graphite ifmeasured in the same direction. Pyrolytic graphite itself is essentiallya highly oriented graphite which has a hexagonal layer structure inwhich the basal planes tend to align themselves parallel to the surfaceof the deposit. As such, pyrolytic graphite conducts electricity bycharge carriers and thermal energy or heat by lattice "ice vibration. Itis believed that the boron alloying material is disposed bothinterstitially and substitutionally in the graphite lattice. As a resultof the boron interstitially deposited between the basal planes ofgraphite, the number of charge carriers for a given area are increasedthereby increasing the potential conductivity of electricity in the samearea. Also, the vibration of each of the basal planes of the pyrolyticgraphite lattice is decreased by the presence of boron therebysuppressing the thermal conductivity of the lattice. It has been foundthat such alloys will transmit current in a direction perpendicular tothe surface of the deposit without an excessive voltage drop while, atthe same time, providing a thermal insulation against the transfer of anexcessive amount of heat.

The alloys of the present invention find wide utility. For example, suchalloys may be used in applications or devices where there is desired acoating or free-standing mass or body capable of withstanding hightemperatures or possessing substantial strength at elevated temperaturesor possessing substantial gas imperviousness or corrosion resistance orpossessing combinations of the above properties. Such alloys may also beemployed so as to utilize the electrical properties thereof. Oneimportant use of such alloys and particularly alloys comprisingpyrolytic graphite and boron is as heat shields. It is often necessaryto adapt delicate instruments or explosive devices with a suitableprotective cover or shield which will insulate them against largechanges in temperatures. A very eifective shield, which may be used forthe purpose may be made of alloys comprising pyrolytic graphite andboron in view of the excellent insulating properties which such alloysexhibit.

Broadly, the precess of this invention comprises contacting at anelevated temperature and a reduced pressure a hydrocarbon gas and avolatile compound (e.g. a halide) of a metal or metalloid such as, forexample, boron, silicon, aluminum, titanium, zirconium, hafnium,thorium, vanadium, niobium, tantalum, molybdenum, tungsten, uranium andthe like to produce an alloy comprising pyrolytic graphite and a metalor an alloy comprising pyrolytic graphite and a metalloid. Thisinvention also comprises a process wherein a suitable substrate iscontacted with a hydrocarbon gas, e.g. methane and a gaseous metalhalide e.g. tungsten halide or a gaseous metalloid halide e.g. boronhalide at an elevated temperature and a reduced pressure therebydepositing an alloy on such substrate. In one embodiment of theinvention, pyrolytic graphite alloys are produced by contacting at anelevated temperature a halogen gas, e.g. chlorine with a mass of a metalor metalloid and immediately thereafter contacting the halide producedwith a gaseous hydrocarbon at an elevated temperature and a reducedpressure. In one preferred embodiment of the invention, alloyscomprising pyrolytic graphite and boron are produced by contacting thevapors of a boron halide, e.g. boron trichloride and a hydrocarbon gas,e.g. methane at a temperature between about 1500 C. and 2300 C. and apressure below about 20 mm. of mercury.

The flow diagram of FIGURE 1 will be described in connection with theproduction of alloys comprising pyrolytic graphite and boron, it beingunderstood that such description is also generally applicable to theproduction of other alloys of pyrolytic graphite.

The substance or substrate desired to be coated is mounted in thereaction furnace 12 which is of the type generally utilized in vapordepositions. The pressure within the furnace is then brought within thepressure range of 20 mm. of mercury or below at which time thetemperature of the furnace is increased from room temperature tosomewhere between about 1500 C. and

2300 C. After the pressure and temperature are established, a gaseoushydrocarbon in the form of methane, natural gas, ethane, propane, orbenzene, from a suitable source or supply 14 is introduced into the feedline 16. This latter line 16 leads to injector 18 which is fitted intofurnace 12 so that the injection end 20 thereof is in proximity to thesubstrate desired to be coated. At this point, a vaporous boron compoundsuch as boron trichloride, which is obtained from a suitable borontrichloride generator or storage tank 22, is fed into the feed line 24.The feed line 24 is adapted with a shut off valve 26 and with valves 28and 30 on either side of flowmeter 32. In this way, relatively true flowvalues are obtained on flow meter 32. The pressure within the furnace isindicated by pressure gauge 34. Line 24 is connected to the injector 18at which point the gaseous reactants are comingled prior to introductioninto the furnace 12. Under the above conditions, the carbon and boronliberated from their respective compounds are deposited on the substrate10 in the form of an alloy comprising pyrolytic graphite and boron. Theformulas which represent the overall process may be set forth asfollows:

( l 3CH pyrolytic graphite+6H (2) 6H +4BCl boron+ l2HCl (3)Boron-j-pyrolytic graphite alloy After a suitable time, i.e. when acoating of desired thickness is obtained, the gaseous reactants are shutoff and the temperature and pressure of the system are allowed to returnto normal. At this point, the substrate which is coated with the alloymay be utilized as such, that is, the substrate may become part of thefinished structure or the substrate may be removed or separated from thealloy coating to form a free-standing alloy mass or body of desiredshape and size.

FIGURE 2 illustrates a halide generating system 36 adapted to producemetal or metalloid halide which is then immediately used in the process.The system 36 has many advantages. For example, it permits theproduction and use of a substantially uncontaminated halide since thehalide once formed is immediately utilized and thus not subjected tocontaminating conditions. Additionally, the system permits easy handlingof the halide and accurate control of the flow of halide vapors.Furthermore, the system eliminates the need for halide storage andeffects economies of operation due to producing the halide andimmediately utilizing it. In this embodiment, a charge of particulate orfinely divided material, for example, sponge, strips, turnings, powder,wire, or the like capable of being converted, i.e. halogenated toproduce the desired metal or metalloid halide for the process, is placedin an enclosed container 40 surrounded by a heater 42 e.g. a resistanceheater capable of heating the material to an elevated temperaturesufficient to affect halogenation thereof, e.g. between about 200 C. and1000 C. Within the container 40, the material 381s confined between aporous support plate 41 and a diffusion plate 43. The material 38 maycomprise a metal or metalloid compound capable of being halogenated,e.g. boron carbide or preferably it comprises a metal or metalloidelement selected from the group consisting of boron, silicon, aluminum,titanium, zirconium, hafnium, thorium, vanadium, niobium, tantalum,molybdenum, tungsten and uranium. A halogen, preferably chlorine, isaccurately metered and fed through an inlet 44 and downwardly throughthe heated charge, e.g. niobium metal to produce the halide, e.g.niobium chloride. The halide vapors flow from the heated halogenatoroutlet 46 either to feed line 24 as described above in FIGURE 1 ordirectly to the injector 18.

The process is carried out at a temperature at which a gaseoushydrocarbon will decompose to produce primarily pyrolytic graphiterather than pyrolytic carbon. The latter, when compared with pyrolyticgraphite may be stated to lack strength, density, and imperviousness.The present process, wherein an alloy comprising pyrolytic graphite anda metal and/or metalloid is deposited on a suitably exposed substrate,has been found to be operative when the reactants are maintained at atemperature between about 1500* C. and 2300 C. Althrough the process isoperative at a deposition temperature between about 1500 C. and 2300"C., it is preferred to carry out the process at a temperature betweenabout 1800 C. and 2100 C. It has been found that the process is highlyeffective within the latter range, especially at about 1950 C.

The pressure of the system is used to obtain an even distribution of thegas over the entire surface of the article. Therefore, the pressure ofthe system is dependent to a large extent on the size and shape of thearticle that it is desired to produce. In any case, the process isoperative at pressures up to 20 mm. of mercury. If the pressure isallowed to increase above 20 mm., a large amount of carbonaceous soot isformed in the system. Although the process is operative at pressures upto 20 mm. of mercury it is preferred to carry out the process at apressure below about 10 mm. of mercury. It has been found that theprocess is highly effective at pressures below about 10 mm. of mercuryand that products of high quality are obtained.

The hydrocarbon gas or gases which may be used in this process includeany carbonaceous gas capable of depositing pyrolytic graphite on anexposed surface when subjected to a suitable decomposition temperature.For illustrative purposes, the hydrocarbon gas may be methane, naturalgas, ethane, propane or benzene. The amount of hydrocarbon gas utilizedin the system is dependent on the temperature and pressure of the systemand the properties that are desired in the final product. When alloysrich in pyrolytic graphite are to be produced the ratio of hydrocarbongas to metal halide or metalloid halide is large. For example, whenproducing alloys having a boron concentration between about 0.32 and1.74 percent by weight, the amount of hydrocarbon gas utilized wasbetween and 300 moles to every mole of boron trichloride that wasintroduced into the system. It is also of interest to note that thevelocity of the hydrocarbon gas is dependent on the amount ofhydrocarbon gas utilized in the system.

The metallic or metalloid compound which is introduced into thecarbonaceous gas should be readily vaporized so that the quantityintroduced can be metered and controlled. Boron trichloride is a goodexample of a material which may be utilized because it is a gas at roomtemperature. However, other materials may be used including volatilecompounds of metalloids such as boron and silicon, and volatilecompounds of metals such as, for example, tungsten, tantalum, niobium,molybdenum, vanadium, thorium, uranium, titanium, hafnium, zirconium,aluminum and the like. Preferably the volatile compounds are halides andmore particularly chlorides, For example, there may be utilized thetrichlorides of boron and aluminum, the tetrachlorides of zirconium,hafnium, uranium, silicon, thorium, and titanium, the pentachlorides ofvanadium, niobium, molybdenum and tantalum, and hexachloride oftungsten, or other chlorides of the above. The ratio of metal halide ormetalloid halide to hydrocarbon gas is not fixed but may vary over awide range. The exact ratio utilized at any given time would depend to alarge degree on the amount of metal or metalloid that is desired toplace in the pyrolytic graphite lattice. The amount of metal and/ormetalloid to be added to the pyrolytic graphite lattice may range fromabout 0.001 percent by weight to an amount necessary to produce a metaland/or metalloid rich alloy. Preferably, however, the total amount ofmetal and/or metalloid added to the pyrolytic graphite lattice rangesfrom about 0.01 percent by weight to about 5.0 percent by weight. itshould be mentioned that pyrolytic graphite alloys may be formedcontaining only one metal or metalloid, or two or more metals ormetalloids or a mixture of at least one metal and at least onemetalloid.

The alloys of the present invention may be used in the form of coatingsor as free-standing bodies or masses of any suitable size and shape. Forexample, the exterior surfaces of a device to be insulated against largechanges in temperature may be protectively coated with a suitablethickness of, for instance, an alloy comprising pyrolytic graphite andboron. Likewise, a free-standing shape may be obtained by coating asuitable substrate, e.g graphite with a desired thickness of a pyrolyticgraphite alloy and thereafter removing the substrate. For example, theinterior surface of a graphite tube may be coated with a suit-ablethickness of a pyrolytic graphite alloy and the graphite thereafterremoved so as to form a free-standing alloy tube. Coherent deposits ofan alloy of various thicknesses may be built up on, for example, fiatplates or discs so as to form fiat stock of alloy which may be utilizedas such or modified as by machining to other shapes. It should also bementioned that by using fluid bed or rotating drum techniques,particulate bodies or masses which can withstand temperatures above 1500C. can likewise be coated with an appropriate pyrolytic graphite alloy.For instance, nuclear fuel particles, e.g. uranium dicarbide, may becoated with a suitable thickness of, for example, an alloy comprisingpyrolytic graphite and zirconium or niobium. Likewise, particles ofnon-conducting materials may be coated with a suitable thickness of, forexample, an alloy comprising pyrolytic graphite and boron. Such coatedparticles may be used in, for instance, resistance elements, e.g.resistors. Among the non-conducting base -material which may thus becoated, mention may be made of ceramic materials such as glass, oxides,such as silica, magnesia, alumina and the like. Whenever the termsubstrate is used in the specification and claims, it is to be taken inits broadest sense and to include within its meaning substances, masses,bodies, material or the like of any size and shape.

More detailed descriptions of producing pyrolytic graphite alloys aregiven in the following non-limiting examples set forth for the purposeof illustration.

Example I A graphite substrate having a flat deposition surf-ace wasplaced in position in a furnace of the type heretofore described and thefurnace was subjected to a pressure of about 8 mm. of mercury, thetemperature of the furnace was then raised to 1950 C. and then methanewas introduced into the injector at a flow rate of 5 liters per minute.After the methane fiow had stabilized itself, boron in the form of borontrichloride was fed into the injector at which time it was comingledwith the hydrocarbon gas. The flow rate of the boron halide wasapproximately 0.03 liter per minute. After the desired deposit thicknesswas obtained, the reactants were turned off and the furnace was allowedto return to room temperature. The substrate was removed from the alloycoating and specimens of the resulting fiat alloy plate were then testedand compared with similar flat plate specimens containing only pyrolyticgraphite. Unless other wise indicated, the property data set forth inthe following tables is at room temperature. It should be noted that thealloy property data set forth hereinafter represents only initial orpreliminary values.

1 Contains 1.74% boron.

Numerous experiments were carried out utilizing the procedure set forthin Example I but in each case the conditions were varied as set forth inTable II which follows:

TABLE II Reactor Gas Flow, l./min. Pressure, p.s.i. Temp, Press,

mm. CH4 B01 CH BCI;

The above Table II illustrates that the process conditions may be variedover a wide range but, in each experiment, a similar coating wasproduced by the process.

Table III, which follows, sets forth the change in propertiesencountered when the boron content of an alloy is varied. The propertydata set forth in Tables III, IV, V, VI and VII for pyrolytic graphiterepresent-s average values.

TABLE III Alloy, percent by weight boron Density (g1u./cc.) 2. 21 2. 222. 21 2. 20 Electrical resistivity (ohm-cm):

c 0. 0266-0. 02679 0. 0189 0.70 a 243 10' 26BX10 284Xl0' sooxro- Bendstrength (p.s.i.) a 37,000 33,000 18,000 Flexure modulus of elasticity(p.s.i.)

10 a 3. 78 6. 78 6. 82 4. 0 Thermal conductivity (B.t.u.-ft./ Itfl-hr,F.):

As compared to unalloyed pyrolytic graphite, the alloys comprisingpyrolytic graphite and boron showed significantly higher bend strengthsthan pyrolytic graphite alone, as well as substantially lower a and cdirection electrical resistivity and c direction thermal conductivity.

Although only pyrolytic graphite alloys having a boron content ofbetween about 0.32 percent to about 1.74 percent by weight have beenexemplified above, it should be mentioned that the boron content may bemore or less, the preferred boron concentrations ranging from about 0.01percent by weight to about 5.0 percent by weight.

The production of other pyrolytic graphite alloys is exemplified in thefollowing examples:

Example 11 A series of runs were made to produce flat plate alloymaterials comprising pyrolytic graphite and niobium. In these runs, achlorinator such as illustrated in FIGURE 2 was employed to form niobiumchloride which was immediately fed to the deposition furnace andutilized. In carrying out these runs the container 40 of halidegenerating system 36 was charged with a suitable quantity of sponge,strips, wire or the like of niobium metal 38 and a graphite substrate 10having a fiat deposition surface was placed in position in a furnace 12of the type as heretofore described. The metal charge 38 in container 40was brought up to a temperature on the order of about 400 C. while thetemperature within the furnace 12 was raised to between about 2130 C.and 2150 C. Methane was introduced into the injector 18 at a flow rateof 3 liters per minute. Chlorine gas was introduced through inlet pipe44 of the system 36 and brought into contact with the heated niobiumcharge. The niobium chloride vapors produced were fed via outlet pipe 46and feed line 24 into the injector 18 at which time they were comingleglwith the methane and the mixture introduced into the furnace. The outletpipe, feed line and injector were heated to a temperature between about295 C. and 320 C. The flow rate of chlorine gas and the chlorinationtemperature were controlled so that the flow rate of niobium chloride tothe injector and the furnace was maintained between about 0.01 and 0.02liter per minute. During the deposition of the alloy on the heatedsubstrate, the pressure within the furnace was maintained at about 5 mm.of mercury. After a suitable deposition time, the chlorine and methaneflows were terminated and the furnace allowed to return to roomtemperature. In the runs carried out the deposition times ranged fromabout 19 hours to about 24 hours to produce alloy coatings having athickness of from about 54 mils to about 90 mils. In each run, thesubstrate was removed from the alloy coating and specimens of theresulting flat plate were examined and tested. Table IV which followsindicates the alloys produced in the above series of runs and some ofthe properties thereof.

TABLE IV Alloy Bend Knoop hardness, Electrical resistivity, content,strength 100 gram tester ohm-cm. percent (p.s.i.) niobium a c a c a 0.0018,000 84. 20. 0 0 700 500 10- 0.14 27,200 107, 26. 9 550 0.23. 27,650113.7 24.0 540 10- 24,125 111.5 31.6 550X10- 23, 200 101.0 23. 8 0. 642509x10- 17, 935 121. 5 30. 2 0.550 580 10- 18, 000 103. 5 25. 0 0. 605480 10- 700 95. 5 31. 0 0. 542 473X10 13,700 97. 9 37. 4 0. 530 463 10-19, 200 112. 5 32. 8 483X 10- As compared to unalloyed pyrolyticgraphite, the alloys comprising pyrolytic graphite and niobium showedincreases in bend strengths especially at low alloy contents, i.e. lessthan 0.5 percent as well as significant gains in a and c directionhardness.

A series of runs similar to Example IV were made to produce fiat platealloy material comprising pyrolytic graphite and molybdenum. However, inthese runs the container 40 was charged with strips, chunks or the likeof molybdenum metal and the deposition times ranged from about 20 to 30hours to produce alloy coatings having a thickness of from about 59 milsto about 105 mils. Table V which follows indicate the alloys producedand some of the properties thereof.

TABLE V Bend Knoop hardstrength ness 100 gram Alloy content,

Electrical resistivity percent molyb- A series of runs similar toExample IV were made to produce flat plate alloy material comprisingpyrolytic graphite and tungsten. However, in these runs, the container40 was charged with sponge, strips or the like of tungsten metal, thechlorinator temperature was maintained between about 395 C. and about440 C., the

methane flow rates were 4 liters per minute, and the deposition timeswere on the order of about 50 hours to produce coatings having anaverage thickness of about 180 mils.

Table VI indicates the alloys produced and some of the propertiesthereof.

a and c direction hardness and in some cases, slightly higher bendstrengths.

A run similar to Example IV was made to produce flat plate alloymaterial comprising pyrolytic graphite and aluminum. However, in thiscase, the container 40 was charged with sponge, strips or the like ofaluminum metal, the methane flow rate was 3 liters per minute while thealuminum chloride flow rate was 0.05 liter per minute and the depositiontime was 50 hours which resulted in a coating having an averagethickness of about 169 mils. Table VII indicates the alloys produced andsome of the properties thereof.

TABLE VII Alloy con- Knoop hardness, 100 Electrical resistivity,

tent, per- Bend gram tester ohm-em.

cent strength aluminum (p.s.i.) a c a c a 18, 000 84. 0 20 0 0. 70500X10 21, 400 98.4 24 7 0. 900x10- 27, 000 84. 8 27 4 0.88 5625x10- Thecontent or concentration of metal or metalloid alloying material can bevaried by suitable control of the reaction mix of hydrocarbon and metalor metalloid halide. Thus, although only pyrolytic graphite alloyshaving a metal or metalloid content of between about 0.002 percent toabout 3.70 percent by weight have been exemplified in the several tablesabove, it is obvious that the content of the alloying material mayextend over a wider range and that if desired alloys containing higherpercentages of metal or metalloid than those illustrated can be readilyprepared. Likewise, although the pyrolytic graphite alloys exemplifiedcontain only a single metal or metalloid, it is evident that alloyscontaining two or more alloying materials may be produced by introducingtwo or more halides in suitable ratios into the furnace with thehydrocarbon.

As various changes may be made in the form, construction and arrangementof the parts herein described without departing from the spirit andscope of the invention and without sacrificing any of the advantages, itis understood that all matter herein is to be interpreted asillustrative and not in a limited sense.

What is claimed is:

1. The process of coating a substrate at a temperature between about1500 C. and 2300 C. and a pressure below about 20 mm. of mercury with agaseous hydrocarbon and a volatile halide of an element selected fromthe group consisting of silicon, aluminum, titanium, zirconium, hafnium,thorium, vanadium, niobium, tantalum, molybdenum, tungsten and uraniumthereby depositing pyrolytic graphite and an element in the form of analloy on said substrate.

2. A pyrolytic graphite alloy produced by contacting at a temperaturebetween about 1500 C. and 2300 C. and a pressure below about 20 mm. ofmercury a gaseous hydrocarbon and a volatile halide of an elementselected from the group consisting of silicon, aluminum, titanium,zirconium, hafnium, thorium, vanadium, niobium, tantalum, molybdenum,tungsten and uranium.

3. The process of producing a pyrolytic graphite alloy which comprisescontacting at a temperature between about 1500 C. and 2300 C. and apressure below about 20 mm. of mercury a gaseous hydrocarbon and avolatile halide of an element selected from the group consisting ofsilicon, aluminum, titanium, zirconium, hafnium, thorium, vanadium,niobium, tantalum, molybdenum, tungsten and uranium.

4. The process of producing a pyrolytic graphite alloy which comprisescontacting at a temperature between about 1500 C. and 2300 C. and apressure below about 20 mm. of mercury a gaseous hydrocarbon and avolatile chloride of an element selected from the group consisting ofsilicon, aluminum, titanium, zirconium, hafnium, thorium, vanadium,niobium, tantalum, molybdenum, tungsten and uranium.

5. The process of producing a pyrolytic graphite alloy which comprisescontacting at an elevated temperature a halogen gas with a mass of anelement selected from the group consisting of silicon, aluminum,titanium, zirconium, hafnium, thorium, vanadium, niobium, tantalum,molybdenum, tugnsten and uranium, and immediately thereafter contactingthe halide produced with a gaseous hydrocarbon at a temperature betweenabout 1500 C. and 2300 C. and a pressure below about 20 mm. of

mercury.

6. The process of claim wherein said halogen gas comprises chlorine.

7. The process of producing an alloy of consisting essentially pyrolyticgraphite and boron which comprises subjecting a reaction mixtureconsisting of gaseous hydrocarbon and boron trichloride to a temperaturebetween about 1500 C. and 2000 C. and a pressure below about 20' mm. ofmercury.

8. The process of producing an alloy of consisting essentially pyrolyticgraphite and boron which comprises subjecting a reaction mixtureconsisting of methane and boron trichloride to a temperature betweenabout 1500 C. and 2000 C. and a pressure below about 20 mm. of

mercury.

References Cited UNITED STATES PATENTS 2,671,735 3/1954 Grisdale et a1.117-46 X 2,764,510 9/1956 Ziegler 1l7-46 X 2,810,365 10/1957 Keser 11746X 2,810,664 10/1957 Gentner 117226 OTHER REFERENCES Grisdale et al.:Pyrolytic Film Resistors, Carbon and Borocarbon, in Bell SystemTechnical Journal 30, pp. 305-313, April 1951.

Mellor: Comprehensive Treatise on Inorganic and Theoretical Chemistry,vol. 5, pp. 129-130, 1924.

RALPH S. KENDALL, Primary Examiner A. GOLIAN, Assistant Examiner US. Cl.X.R.

1. THE PROCESS OF COATING A SUBSTRATE AT A TEMPERATURE BETWEEN ABOUT1500*C. AND 2300*C. AND A PRESSURE BELOW ABOUT 20MM. OF MERCURY WITH AGASEOUS HYDROCARBON AND A VOLATILE HALIDE OF AN ELEMENT SELECTED FROMTHE GROUP CONSISTING OF SILICON, ALUMINUM, TITANIUM, ZIRCONIUM, HAFNIUM,THORIUM, VANADIUM, NIOBIUM, TANTALUM, MOLYBDENUM, TUNGSTEN AND URANIUMTHEREBY DEPOSITING PYROLYTIC GRAPHITE AND AN ELEMENT IN THE FORM OF ANALLOY ON SAID SUBSTRATE.